Pentax held a brief in Tokyo on the 9th, before the sales started today.
This article on DCWatch goes into the history behind the 645D launch -
http://dc.watch.impress.co.jp/docs/news/20100610_373415.html
One of the reasons for the delay was that they wanted to get the K-7 out of the door before finalizing the 645D.
Among other things they mention that Pentax tried a CMOS sensor with live view but decided that the better image quality offered by the CCD was more important than offering a live view.
It seems as if the sensor assembly can accept a low-pass filter that might be included if there is a demand. It would be rather expensive though, that's why it is not there now, if I understand them correctly. Hopefully, this makes more sense to you…
They offer several reasons for adopting the SDHC card and not the SDXC. The two slots can be used in several different ways, one RAW and the other JPEG, or one used as a backup for the other, just to mention a few.
The shutter should last 50,000 exposures, these are actually counted in the camera.
Costs were controlled by sharing about 10% of the components with the K-7, for example PRIME-II and the battery. This should give between 650 and 800 exposures, depending on the temperature.
The lens road map was not revealed in detail but the super-wide-angle lens shown earlier should come.
They don't target the professional or the overseas customer now. The order situation is said to be extremely good. Overseas deployment is depending on the establishment of after-sales service.